DESCRIPTION: Dilated cardiomyopathy is a disease of the heart that in most cases leads to decreased cardiac function and eventually to congestive heart failure. Mechanical factors such as stress and strain have been implicated as regulatory factors in diseases such as cardiac hypertrophy. The overall hypothesis of this proposal is that mechanical factors play a significant role in the tissue remodeling associated with dilated cardiomyopathy and cardiac failure. Sophisticated computational models in conjunction with experimental studies in rodents with different etiologies of heart failure (both genetic and surgically-induced) will help elucidate the role of mechanical factors in the progression of cardiac dilation and failure. The following hypotheses will be tested: (1) Dilated cardiomyopathy and eventual heart failure are mediated by mechanical loads on the heart, and the transition from a compensated hypertrophic state to cardiac failure is dependent on a critical level of stress or strain. Studies of cardiac function before and after this transitory phase can determine which mechanical factors are important. (2) A change in residual stress has important consequences for regional function in the heart, and may be a mechanism of dysfunction in heart failure. We will investigate this possibility by quantifying geometry and tissue structure in the stress-free state of the ventricle during the transition from dilation to failure, and use mathematical models to predict subsequent abnormal changes in diastolic and systolic wall stresses. (3) We expect that changes in. regional myocyte orientation, both at the cellular and global levels, are mechanisms of cardiac dilatation and failure. To test this hypothesis, local myocyte disarray and regional variations in laminar sheet orientation will be measured during the transition to failure. We will incorporate these measures into computational models of the heart, and then independently alter the myocyte orientation in the model, and compare the functional results with those obtained experimentally. We propose that these regional structural changes accompanies dilatory heart failure, and are mechanisms behind the reduction in fiber shortening and the ability of the wall to thicken during systole.